1 Field of the Invention
The invention relates, in general, to a stopper assembly for use with a syringe and, more particularly, to a stopper assembly manufactured from a rigid or semi-rigid plastic material that provides an active sealing function.
2 Description of Related Art
Current syringe designs can typically be categorized as two-piece syringes or three-piece syringes. A typical three-piece syringe includes a tubular barrel having an access opening formed at one end, and a smaller discharge opening formed at the opposing end. The lead end of an elongated plunger is received within the access opening of the barrel so as to be slidable within the barrel. Attached to the lead end of the plunger is a flexible sealing member or stopper that snugly seals against the interior surface of the barrel. A needle, a threaded member, or a non-threaded member is usually attached to the discharge opening on the barrel. The needle can be used to penetrate a surface while the threaded member can be used to attach the syringe to another medical device, such as a catheter. The flexible stopper is usually manufactured from an elastomeric material, such as a rubber or a cross-linked or thermoplastic elastomer.
A two-piece syringe, on the other hand, includes a “stopper” that is in the form of a rigid sealing disc, also known as a plunger rod head. It is typically made of the same rigid plastic as the rest of plunger rod. The sealing force in a two-piece syringe comes from a thin elastic barrel that deforms around the rigid plunger rod head.
During use, the discharge end of the syringe is initially placed in contact with a fluid. For example, the needle on the syringe can be inserted into a liquid medication. As the plunger is retracted within the barrel, a process known as aspiration, a negative pressure is formed within the end of the barrel so as to cause the fluid to be drawn into the barrel. The syringe can then be moved to a second location where advancing the plunger within the barrel causes the fluid to be pushed or expressed out the discharge end of the barrel.
Current two-piece and three-piece syringe designs suffer from various deficiencies. For instance, three-piece syringes that include an elastomeric or rubber stopper have a high passive contact pressure between the stopper and syringe barrel that is present during the shelf life and when the syringe is in use. This passive contact pressure can be as high as approximately 300 psi or more. Accordingly, the syringe barrel requires relatively large barrel wall thickness in order to prevent localized barrel creep or bulging during the shelf life. Therefore, a need exists for a syringe that has a lower contact pressure between the stopper and the barrel such that localized bulging of the syringe barrel is eliminated. Typical two-piece syringes also include such high passive contact pressures and suffer from similar deficiencies. Therefore, a need exists for a syringe manufactured using less material to achieve thinner walls by addressing the bulging effect caused by current stopper designs.
In addition, due to the high contact forces and high friction coefficient between current elastomeric or rubber stoppers and the inner wall of the barrels, current syringe designs must be lubricated with a liquid lubricant, such as silicone oil, so that break-loose and break-out hand forces required to operate the syringe are not too high. Accordingly, a need further exists for a plastic stopper that can be used with a syringe without silicone oil or other lubricants or that allows for significantly lower hand forces when used with a lubricant.
Furthermore, current rubber stoppers are typically manufactured from a specialized cross-linked rubber (e.g., polyisoprene) that requires a specialized compression molding/curing process. Such a process can significantly increase the cost of manufacturing the syringe. Furthermore, significant waste materials are also produced during the compression molding process. For example, in a typical manufacturing process, up to 30% of the rubber is discarded during manufacturing of the conventional elastomeric stopper. Accordingly, a need exists for a stopper that can be efficiently manufactured, thereby reducing the cost of manufacturing the syringe and reducing the waste materials produced during the manufacturing of the syringe.
Conventional two-piece syringes also suffer from a variety of deficiencies. More particularly, conventional two-piece syringes typically include rigid plunger rod sealing edges. Such edges create very high contact forces which increase the hand force necessary to move the plunger. In addition, these high contact forces along the sealing edges significantly deform the barrel walls, which make two-piece syringes incompatible with syringe pumps where the barrel bulge can interfere with a pump clamping mechanism. Accordingly, a need exists for a syringe that has a lower contact pressure between the stopper and the barrel such that localized bulging of the syringe barrel is eliminated.